1. Field of the Invention
This application concerns a method to control an overactive bladder and to estimate bladder volume, comprising an implanted sensor, which sensor comprises at least one nerve electrode to sense electrical signals, means for stimulation of nerves to inhibit detrusor contraction, an electronic unit to detect events from nerve signals and generate electrical pulses for stimulating nerves.
2. Description of the Related Art
U.S. Pat. No. 4,406,228 discloses a system that purportedly conditions pelvic floor musculature by means of neurostimulation for the purpose of controlling urinary loss. Such system includes stimulation apparatus for applying electrical pulses to electrodes implanted in the abdominal region or to a plug positioned in an anus. The plug contacts the spincter muscle of the anus for the alleged purpose of inhibiting bladder contraction in response to excitation of the plug.
In this way the bladder volume is not measured, which can lead to bladder over distensions, and can lead to bladder rupture.
The storage phase of the micturition cycle requires a stable bladder with high compliance (i.e. a relaxed bladder) and closed urethral outlet. However, due to the feedback system the bladder may easily become unstable. Any stimulus that elicits a small burst of impulses in the mechanoreceptor afferents, such as coughing and jumping, may trigger an involuntary micturition reflex and cause urine leakage. To prevent this from happening, the neural control system is equipped with several inhibitory circuits, both at spinal and supraspinal levels, which prevent the detrusor muscle from contracting. However, these inhibitory circuits are susceptible to a variety of neurologic disorders. Therefore, patients with neurologic disorders frequently suffer from urinary incontinence due to involuntary detrusor contractions.
The impaired storage function could in principle be improved by methods that decrease the sensitivity of the bladder afferents, decrease the activity of the bladder efferents or increase the bladder volume/capacity. Available treatment options are therefore: surgical augmentation of the bladder [Sidi et al., 1990], surgical deafferentation of the bladder [Koldewijn et al., 1994], the use of anticholinergic drugs and the use of intravesical capsaicin [Wiart et al., 1998].
Bladder inhibition by electrical stimulation has been described before [e.g. Vodu{hacek over (s)}ek et al., 1988; Wheeler et al., 1992] but only continuous stimulation was used, i.e. stimulation is permanent except during voiding.
The objects of the invention are:
1) treatment of involuntary loss of urine (incontinence) due to involuntary detrusor contractions (detrusor overactivity)
2) estimation of bladder volume. This finds particular application in patients who use aids to empty their bladder e.g. intermittent catherisation or electrical stimulation.
The invention finds particular application in patients where the involuntary detrusor contraction is associated with a neurologic disorder.
Treatment of detrusor overactivity and estimation of bladder volume can be achieved by a method as described in the first paragraph using a closed loop stimulation system to allow event-driven inhibition of the bladder where stimulation is only applied when an undesired bladder contraction occurs, and an implanted sensor comprising at least one nerve electrode to sense electrical signals from nerves innervating the bladder. Sensing electrical signals related to mechanical bladder activity via said sensor, the method detects the onset of a bladder contraction and estimates bladder volume using signal processing methods, activating an inhibitory neural circuit by stimulating afferent nerve fibers.
By this method no nerves have to be cut, and no irreversible surgery has to be done. Stimulation of neural tissue only takes place when needed, and the volume of the bladder is monitored. The present invention uses electrical stimulation to inhibit the bladder. Inhibition of the bladder by electrical stimulation is possible since, besides the mentioned neural inhibitory circuits, additional spinal inhibitory circuits exist to prevent involuntary leakage during, e.g., defecation, coitus and physical activity. Activation of the afferent paths of these neural circuits has two effects: they activate the in hibitory sympathetic neurons to the bladder and they provide central inhibition of the preganglionic detrusor-motoneurons through a direct route in the spinal cord. These additional inhibitory reflexes are not suppressed during micturition, which means that they are quite capable of interrupting a detrusor contraction. Activation of these reflexes by electrical stimulation is a nondestructive alternative method for patients who are refractory to drugs, cannot tolerate the side effects or for other reasons do not accept a drug treatment.
Primarily, the recorded nerve signals come from afferents innervating mechanoreceptors located in the bladder wall. By detecting the onset of the bladder contraction, the stimulator can be activated only when contraction occurs, and continuous stimulation is not necessary. This minimises the risk of neural damage due to the stimulation. In addition, if the patient can sense the stimulation, the duration of stimulation should be minimised to minimise the discomfort.
The step of implanting a sensor might comprise the step of implanting a nerve cuff electrode. The intrafasicular electrode is flexible and small, and may be preferred in locations where limited space is available.
The step of implanting a sensor might comprise the step of implanting an intrafasicular electrode [Lefurge et al., 1991]. The intrafasicular electrode is flexible and smaller, and might be preferred in locations where limited space is available.
The electrodes can be used to detect efferent or afferent nerve activity. The same electrode could be used to record both types of nerve signals.
The electrode can be placed on a nerve that contains afferent nerve fibres innervating mechanoreceptors located in the bladder. In this way information about the status of the bladder can be obtained.
The electrode can be located at the intradural or extradural dorsal sacral nerve roots. In this way the electrodes can be placed at a mechanically stable position, and the nerve roots are relatively long, which enables easy placement of electrodes.
The electrode can be placed on a nerve that contains efferent nerve fibres innervating the bladder, so bladder activation can be monitored.
The electrode can be located at the intradural or extradural ventral sacral nerve roots. In this way the electrodes can be placed at a mechanically stable position, and the nerve roots are relatively long, which enables easy placement of electrodes.
The electrode might be located at at least one of the preganglionic pelvic nerve branches and postganglionic nerve branches. In this way nerve signals from the bladder can be recorded more selectively without contamination with signals from other organs.
Preferably two different nerve signals can be used to detect a detrusor contraction, where the first signal comes from afferent nerves innervating the bladder, and the second signal comes from efferent nerves innervating the detrusor muscle. In this way the detrusor contraction can be detected more reliably.
Activating a neural circuit that inhibits the bladder contraction can be done by stimulating afferent nerve fibres, innervating mechanoreceptors, located in the glans of the penis or clitoris. In this way an ongoing detrusor contraction can be aborted or stopped and leakage of urine will be prevented.
The bladder volume can be derived from the amplitude of the recorded afferent signal. By measuring of the bladder volume the patient can be informed about his/her bladder volume.
The bladder volume can be derived from the time between two consecutive detrusor contractions. By measuring of the bladder volume, the patient can be informed about his/her bladder volume.
The bladder volume can be derived from both the amplitude of the recorded nerve signal and the time between two consecutive detrusor contractions. This way the bladder volume can be estimated in a more reliable way.
In the following the invention will be detailed described partly with reference to drawings.